Clifford richardson



CLIFFORD RICHARDSON, OF NEIV YORK, N. Y., ASSIGNOR TO THE BARBER ASPHALTPAVING COMPANY, OF SAME PLACE.

AS PHALTIC PAVEM ENT.

SPECIFICATION forming part of Letters Patent No. 607,884, dated July 26,1898.. Application filed February 4, 1897. erial No- 622,023- (ITspecimenso Patented in England April 12, 1897, No. 9,315.

To all whom it may concern.-

Be it known that I, CLIFFORD Rronnnnson, a citizen of the United States,residing in the city, county, and State of New York, have inventedcertain new and useful Improvements in Asphaltic Pavements, (for which Ihave obtained Letters Patent in Great Britain, No. 9,315, dated April12, 1897,) of which the following is a specification.

This invention relates to that well-known class of asphalt pavements inwhich a natural or artificial bitumen, or both combined, is mixed with amineral aggregate of sand, either silicious or calcareous, and finemineral dust or hydraulic cement for the purpose of making a bituminousconcrete, which when properly combined, laid, and compressed shall forma pavement-surface.

Asphalt pavements have been laid for many years under different formulaeby many different parties; but heretofore it has never been foundpracticable to produce pavements uniform in character. It has been foundby all of those who have engaged in this business that pavements laidupon the same formula will not be alike, that some will be excellent inquality, durable, and in every way effective, while others laid upon thesame formula will fail to come up to the standard requirements in manyrespects. Many efforts have been made from time to time to discover thecause of this difference in pavements of the same composition ofmaterials, but without success. In the course of many experiments andtrials I have discovered that the grading of the sand in a pavingcomposition is not,

as heretofore supposed, a mere matter of con venience and dependent uponthe particular kind of sand used, but that it is a matter which isabsolutely essential to secure a pavement of uniform quality, and I havediscovered that by properly grading the sand, as I shall hereinafter setforth, using other materials in proper and in most cases well-knownproportions, I am enabled to lay pavements which shall be substantiallyalike in all respects and to adopt a formula with the positive knowledgeas to the character of the pavement which will result therefrom. I havefurther discovered that by properly grading the sand I am enabled tocombine effectively therewith a larger proportion of bitumen Withoutmaking a pavement that will become too soft and liable to creep, whilesecuring a greater degree of toughness and pliability than hasheretofore been practicable with pavements of requisite durability. Forthe purpose of regulating the sizes of the particles of the mineralaggregate,

of which the mixtures consist to which this invention relates, a seriesof sieves is employed, which'are made with a sifting portion of brasscloth of the numbers commonly known in the trade as Nos. 10, 20, 30, 40,50, 80, 100, and 200 mesh and which pass particles having on the averagea diameter of .085, .17, .24, .32, .50, .67, one, and two millimeters.This series is selected because the average diameters of the largestparticles passed by the different sieves bear a numerical relation toeach other, being about one, two, three, four, six, eight, twelve,twenty-four, the size of the largest particle passed by the smallestsieve being taken as unity; but any other se ries of sieves could beusedin place of these with the same objects in View, if they pass particleswithin the same extreme limits of size. With these sieves the grading ofthe mineral matterin an asphalt pavement-or of the sand and dust ofwhich it is composed can be determined and represented in percentages,as hereinafter illustrated.

Experience with such pavements as have worn the best shows that theyhave accidentally been made with sand containing but a small proportionof coarser-sized particles. Further experimental tests have shown methat it is desirable to have the mineral aggregate rich in particles ofthe size passing the two-hundred, one-hundred, and eighty mesh sieves,and I have also found that mineral aggregates which contain much finematerial will carry more bitumen, will prove more dense and compact, andwill have better wearing properties than those made of coarser materialand which will carry less bitumen.

The present improvement in the making of asphaltic pavements consists,therefore, in the grading of the mixture of sand and dust (by dust Imean any earthy matterthat will too pass through a sieve having at leastone hundred meshes to the inch) by means of sifting and Varying theproportions of the material employed, so that the resulting surfacemixture shall contain at least thirty-five per cent. and preferably alarger amount of material which will pass an eighty-mesh sieve. Thegrading of this thirty-five per cent. or more of sand in the mixture ispreferably as follows: ten per cent. or more passing a two-hundredmeshsieve or smaller than .085 millimeters in I average diameter; ten percent. or more passing a one-hundred-mesh sieve, but not a twohundred;fifteen per cent. or more passing an eighty-mesh sieve, but not aone-hundred.

Not more than fifteen per cent. of the material used should be so largeas to fail to pass a forty-mesh sieve, preferably less, and but a smallamount, or none, should fail to pass the ten and twenty mesh sieves. Incombination with such graded mineral aggregates I add the bituminouscement in such amount as to give over 10.5 per cent. (and preferablymore) pure bitumen, soluble in carbon bisul fid, or as much aswell-known tests will show that the mixture will carry Without becomingsloppy when, hauled upon the work.

As an illustration of one of the best graded mixtures made according tomylinvention the following will serve: bitumen, 11.10; passingtwo-hundred mesh, 15.30; one-hundred mesh, 12.70; eighty mesh, 20.50;fifty mesh, 33.70; forty" mesh, 3.60; thirty mesh, 1.50; twenty mesh,1.10; ten mesh, .50.

No asphalt-paving surfaces have ever been laid heretofore whichcontained these high percentages of bitumen and graded fine mineralmatter; and this is the important feature of my discovery-that is, notonly that the mineral matter shall be graded, but that by thus gradingit I am enabled to employ so much larger a proportion of bitumen thanhas ever heretofore been efiectively used.

Having thus described my invention, what I claim, and desire to secureby Letters Patent, is

1. An artificial-pavement composition containing bitumen and mineralmatter, in which the latter contains predetermined proportions ofdifferent grades, at least thirty-five per cent. of the mineral matterconsisting of particles capable of passing-at least ten per cent.through'a tWo-hundred-mesh sieve, at least ten per cent. through aone-hundredmesh sieve, and at least ten per cent. through theeighty-mesh. sieve, substantially as described.

2. An artificial-pavement composition containingbitu men and mineralmatter, in which the latter contains predetermined proportions ofdifferent grades, as specified, and the proportions of bitumen exceeds10.5 per cent., substantially as described.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

CLIFFORD RICHARDSON.

WVitnesses:

W. CLARENCE DUvALL, G. P. KRAMER.

